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import math
import torch
import torch.nn as nn
import torch.nn.functional as F
import torch.utils.checkpoint as cp
from mmcv.cnn import build_conv_layer, build_norm_layer
from ..builder import BACKBONES
from ..utils import ResLayer
from .resnet import Bottleneck as _Bottleneck
from .resnet import ResNetV1d
class RSoftmax(nn.Module):
"""Radix Softmax module in ``SplitAttentionConv2d``.
Args:
radix (int): Radix of input.
groups (int): Groups of input.
"""
def __init__(self, radix, groups):
super().__init__()
self.radix = radix
self.groups = groups
def forward(self, x):
batch = x.size(0)
if self.radix > 1:
x = x.view(batch, self.groups, self.radix, -1).transpose(1, 2)
x = F.softmax(x, dim=1)
x = x.reshape(batch, -1)
else:
x = torch.sigmoid(x)
return x
class SplitAttentionConv2d(nn.Module):
"""Split-Attention Conv2d in ResNeSt.
Args:
in_channels (int): Number of channels in the input feature map.
channels (int): Number of intermediate channels.
kernel_size (int | tuple[int]): Size of the convolution kernel.
stride (int | tuple[int]): Stride of the convolution.
padding (int | tuple[int]): Zero-padding added to both sides of
dilation (int | tuple[int]): Spacing between kernel elements.
groups (int): Number of blocked connections from input channels to
output channels.
groups (int): Same as nn.Conv2d.
radix (int): Radix of SpltAtConv2d. Default: 2
reduction_factor (int): Reduction factor of inter_channels. Default: 4.
conv_cfg (dict): Config dict for convolution layer. Default: None,
which means using conv2d.
norm_cfg (dict): Config dict for normalization layer. Default: None.
dcn (dict): Config dict for DCN. Default: None.
"""
def __init__(self,
in_channels,
channels,
kernel_size,
stride=1,
padding=0,
dilation=1,
groups=1,
radix=2,
reduction_factor=4,
conv_cfg=None,
norm_cfg=dict(type='BN'),
dcn=None):
super(SplitAttentionConv2d, self).__init__()
inter_channels = max(in_channels * radix // reduction_factor, 32)
self.radix = radix
self.groups = groups
self.channels = channels
self.with_dcn = dcn is not None
self.dcn = dcn
fallback_on_stride = False
if self.with_dcn:
fallback_on_stride = self.dcn.pop('fallback_on_stride', False)
if self.with_dcn and not fallback_on_stride:
assert conv_cfg is None, 'conv_cfg must be None for DCN'
conv_cfg = dcn
self.conv = build_conv_layer(
conv_cfg,
in_channels,
channels * radix,
kernel_size,
stride=stride,
padding=padding,
dilation=dilation,
groups=groups * radix,
bias=False)
# To be consistent with original implementation, starting from 0
self.norm0_name, norm0 = build_norm_layer(
norm_cfg, channels * radix, postfix=0)
self.add_module(self.norm0_name, norm0)
self.relu = nn.ReLU(inplace=True)
self.fc1 = build_conv_layer(
None, channels, inter_channels, 1, groups=self.groups)
self.norm1_name, norm1 = build_norm_layer(
norm_cfg, inter_channels, postfix=1)
self.add_module(self.norm1_name, norm1)
self.fc2 = build_conv_layer(
None, inter_channels, channels * radix, 1, groups=self.groups)
self.rsoftmax = RSoftmax(radix, groups)
@property
def norm0(self):
"""nn.Module: the normalization layer named "norm0" """
return getattr(self, self.norm0_name)
@property
def norm1(self):
"""nn.Module: the normalization layer named "norm1" """
return getattr(self, self.norm1_name)
def forward(self, x):
x = self.conv(x)
x = self.norm0(x)
x = self.relu(x)
batch, rchannel = x.shape[:2]
batch = x.size(0)
if self.radix > 1:
splits = x.view(batch, self.radix, -1, *x.shape[2:])
gap = splits.sum(dim=1)
else:
gap = x
gap = F.adaptive_avg_pool2d(gap, 1)
gap = self.fc1(gap)
gap = self.norm1(gap)
gap = self.relu(gap)
atten = self.fc2(gap)
atten = self.rsoftmax(atten).view(batch, -1, 1, 1)
if self.radix > 1:
attens = atten.view(batch, self.radix, -1, *atten.shape[2:])
out = torch.sum(attens * splits, dim=1)
else:
out = atten * x
return out.contiguous()
class Bottleneck(_Bottleneck):
"""Bottleneck block for ResNeSt.
Args:
inplane (int): Input planes of this block.
planes (int): Middle planes of this block.
groups (int): Groups of conv2.
base_width (int): Base of width in terms of base channels. Default: 4.
base_channels (int): Base of channels for calculating width.
Default: 64.
radix (int): Radix of SpltAtConv2d. Default: 2
reduction_factor (int): Reduction factor of inter_channels in
SplitAttentionConv2d. Default: 4.
avg_down_stride (bool): Whether to use average pool for stride in
Bottleneck. Default: True.
kwargs (dict): Key word arguments for base class.
"""
expansion = 4
def __init__(self,
inplanes,
planes,
groups=1,
base_width=4,
base_channels=64,
radix=2,
reduction_factor=4,
avg_down_stride=True,
**kwargs):
"""Bottleneck block for ResNeSt."""
super(Bottleneck, self).__init__(inplanes, planes, **kwargs)
if groups == 1:
width = self.planes
else:
width = math.floor(self.planes *
(base_width / base_channels)) * groups
self.avg_down_stride = avg_down_stride and self.conv2_stride > 1
self.norm1_name, norm1 = build_norm_layer(
self.norm_cfg, width, postfix=1)
self.norm3_name, norm3 = build_norm_layer(
self.norm_cfg, self.planes * self.expansion, postfix=3)
self.conv1 = build_conv_layer(
self.conv_cfg,
self.inplanes,
width,
kernel_size=1,
stride=self.conv1_stride,
bias=False)
self.add_module(self.norm1_name, norm1)
self.with_modulated_dcn = False
self.conv2 = SplitAttentionConv2d(
width,
width,
kernel_size=3,
stride=1 if self.avg_down_stride else self.conv2_stride,
padding=self.dilation,
dilation=self.dilation,
groups=groups,
radix=radix,
reduction_factor=reduction_factor,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
dcn=self.dcn)
delattr(self, self.norm2_name)
if self.avg_down_stride:
self.avd_layer = nn.AvgPool2d(3, self.conv2_stride, padding=1)
self.conv3 = build_conv_layer(
self.conv_cfg,
width,
self.planes * self.expansion,
kernel_size=1,
bias=False)
self.add_module(self.norm3_name, norm3)
def forward(self, x):
def _inner_forward(x):
identity = x
out = self.conv1(x)
out = self.norm1(out)
out = self.relu(out)
if self.with_plugins:
out = self.forward_plugin(out, self.after_conv1_plugin_names)
out = self.conv2(out)
if self.avg_down_stride:
out = self.avd_layer(out)
if self.with_plugins:
out = self.forward_plugin(out, self.after_conv2_plugin_names)
out = self.conv3(out)
out = self.norm3(out)
if self.with_plugins:
out = self.forward_plugin(out, self.after_conv3_plugin_names)
if self.downsample is not None:
identity = self.downsample(x)
out += identity
return out
if self.with_cp and x.requires_grad:
out = cp.checkpoint(_inner_forward, x)
else:
out = _inner_forward(x)
out = self.relu(out)
return out
@BACKBONES.register_module()
class ResNeSt(ResNetV1d):
"""ResNeSt backbone.
Args:
groups (int): Number of groups of Bottleneck. Default: 1
base_width (int): Base width of Bottleneck. Default: 4
radix (int): Radix of SplitAttentionConv2d. Default: 2
reduction_factor (int): Reduction factor of inter_channels in
SplitAttentionConv2d. Default: 4.
avg_down_stride (bool): Whether to use average pool for stride in
Bottleneck. Default: True.
kwargs (dict): Keyword arguments for ResNet.
"""
arch_settings = {
50: (Bottleneck, (3, 4, 6, 3)),
101: (Bottleneck, (3, 4, 23, 3)),
152: (Bottleneck, (3, 8, 36, 3)),
200: (Bottleneck, (3, 24, 36, 3))
}
def __init__(self,
groups=1,
base_width=4,
radix=2,
reduction_factor=4,
avg_down_stride=True,
**kwargs):
self.groups = groups
self.base_width = base_width
self.radix = radix
self.reduction_factor = reduction_factor
self.avg_down_stride = avg_down_stride
super(ResNeSt, self).__init__(**kwargs)
def make_res_layer(self, **kwargs):
"""Pack all blocks in a stage into a ``ResLayer``."""
return ResLayer(
groups=self.groups,
base_width=self.base_width,
base_channels=self.base_channels,
radix=self.radix,
reduction_factor=self.reduction_factor,
avg_down_stride=self.avg_down_stride,
**kwargs)
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